The Hundred Years War (1337-1457) witnessed the beginning of national identity and loyalty to the nation-state as a series of dynastic wars served to crystalize national identities. The need for large military forces, including mercenary contingents, gave rise to the replacement of in-kind taxes with regular collections of specie. This, in turn, required the development of a centralized governmental mechanism as the embryonic states began to build a governmental infrastructure controlled by the king. Both during the war and for more than 100 years following it, Europe was plagued by bands of demobilized ex-soldiers who fought for pay and constantly switched sides. The problem was how to bring these military forces under the control of a national army. The solution was permanent pay, regular garrison locations, strict codes of military discipline, and the emergence of military rank and administrative structures. By the 1600s, for the first time since Rome, Europe once again began to develop stable, permanent armed forces directed by central national authorities and supported by taxation.

It was the emergence of a national authority that spurred the organizational, tactical, and technological development of armies during this period, and set the pattern for the next four centuries. A permanent army of professionals could be disciplined and schooled in new battle tactics and trained to utilize the new firearms to great effect. This, in turn, helped stabilize the emergent role of infantry whose musket and pike tactics now permitted thinner linear formations of infantry to be used on the battlefield. The invention and development of the firearm required a disciplined soldier, and this brought into existence a more permanent and articulated rank and administrative structure to train and lead the soldier. Permanent rank and military organization reappeared and, by the time of the Thirty Years War (1618-48), all the major elements of the modern army had been set into place.